Prevalent CD8(+) T cell response against one peptide/MHC complex in autoimmune diabetes

Magnetic separation of melanoma-specific cytotoxic T lymphocytes from a vaccinated melanoma patient's blood using MHC/peptide complex-conjugated bacterial magnetic particles

Target antigen-specific cytotoxic T lymphocytes (CTLs) play a key role in anticancer and antivirus immunity in the body, and purification of CTLs from heterogeneous immune cells is desired for an efficient cancer immunotherapy and fundamental research. Herein, a novel magnetic nanoparticle conjugated with major histocompatibility complex (MHC)/peptide complexes was developed for the magnetic separation of melanoma-specific CTLs. To conjugate biotinylated MHC/peptide complexes on nanosized bacterial magnetic particles (BacMPs), which were synthesized intracellularly by magnetotactic bacteria, phased modification of biotin and streptavidin onto BacMPs was investigated. When biotin was modified on BacMPs, a polyethylene oxide (PEO)-linker contributed to the maintenance of the high dispersion properties of BacMPs. Furthermore, nonspecific binding of BacMPs to cell surface was prevented by controlling the level of streptavidin bound on BacMPs and through PEO blocking of the empty streptavidin sites on BacMPs. Finally, single-step magnetic separation of melanoma-specific CTLs was demonstrated using developed MHC/MAGE-1 A24 peptide complex-conjugated BacMPs. Melanoma-reactive cells and melanoma-specific CTLs were successfully separated from stimulated peripheral blood mononuclear cells derived from a vaccinated melanoma patient with 93.1% and 87.7% purity, respectively, and specificity of antigen recognition and cytokine secretion from separated CTLs were confirmed. The potential of MHC/peptide complex-conjugated BacMPs was indicated for efficient separation of antigen-specific CTLs in cancer immunotherapy and fundamental research.

The role of low avidity T cells in the protection against type 1 diabetes: a modeling investigation

Cytotoxic T lymphocytes (CTLs) play a dominant role in the pathogenesis of autoimmune diabetes, commonly denoted Type 1 Diabetes (T1D). These CTLs (notably CD8(+) T cells) recognize and kill insulin-secreting pancreatic beta cells, reducing their number by approximately 90%. The resulting reduction of insulin secretion causes the defective regulation of glucose metabolism, leading to the characteristic symptoms of diabetes. Recognition of beta cells as targets by CTLs depends on the interactions between MHC-peptide complexes on the surface of beta cells and receptors (TCRs) on T cells. Those CTLs with high affinity TCRs (also called high avidity T cells) cause most of the harm, while those with low affinity TCRs (also called low avidity T cells) play a more mysterious role. Recent experimental evidence suggests that low avidity T cells accumulate as memory T cells during the disease and may be protective in NOD mice (a strain prone to developing T1D), delaying disease progression. It has been hypothesized that such low avidity T cells afford disease protection either by crowding the islets of Langerhans, where beta cells reside, or by killing antigen presenting cells (APCs). In this paper, we explore the hypothesized mechanisms for this protective effect in the context of a series of models for (1) the interactions of low and high avidity T cells, (2) the effect of APCs and (3) the feedback from beta cell killing to autoantigen-induced T cell proliferation. We analyze properties of these models, noting consistency of predictions with observed behaviour. We then use the models to examine the influence of various treatment strategies on the progression of the disease. The model reveals that progressive accumulation of memory low avidity autoreactive T cells during disease progression makes treatments aimed at expanding these protective T cell types more effective close to, or at the onset of clinical disease. It also provides evidence for the hypothesis that low avidity T cells kill APCs (rather than the alternate hypothesis that they crowd the islets).

T-cell promiscuity in autoimmune diabetes

OBJECTIVE

It is well established that the primary mediators of beta-cell destruction in type 1 diabetes are T-cells. Nevertheless, the molecular basis for recognition of beta-cell-specific epitopes by pathogenic T-cells remains ill defined; we seek to further explore this issue.

RESEARCH DESIGN AND METHODS

To determine the properties of beta-cell-specific T-cell receptors (TCRs), we characterized the fine specificity, functional and relative binding avidity/affinity, and diabetogenicity of a panel of GAD65-specific CD4(+) T-cell clones established from unimmunized 4- and 14-week-old NOD female mice.

RESULTS

The majority of GAD65-specific CD4(+) T-cells isolated from 4- and 14-week-old NOD female mice were specific for peptides spanning amino acids 217-236 (p217) and 290-309 (p290). Surprisingly, 31% of the T-cell clones prepared from 14-week-old but not younger NOD mice were stimulated with both p217 and p290. These promiscuous T-cell clones recognized the two epitopes when naturally processed and presented, and this dual specificity was mediated by a single TCR. Furthermore, promiscuous T-cell clones demonstrated increased functional avidity and relative TCR binding affinity, which correlated with enhanced islet infiltration on adoptive transfer compared with that of monospecific T-cell clones.

CONCLUSIONS

These results indicate that promiscuous recognition contributes to the development of GAD65-specific CD4(+) T-cell clones in NOD mice. Furthermore, these findings suggest that T-cell promiscuity reflects a novel form of T-cell avidity maturation.

The proline-rich sequence of CD3epsilon as an amplifier of low-avidity TCR signaling

Engagement of peptide-MHC by the TCR induces a conformational change in CD3epsilon that exposes a proline-rich sequence (PRS) and recruits the cytoskeletal adaptor Nck. This event, which precedes phosphorylation of the CD3epsilon ITAM, has been implicated in synapse formation and T cell function. However, there is compelling evidence that responsiveness to TCR ligation is CD3epsilon PRS independent. In this study, we show that the CD3epsilon PRS is necessary for peptide-MHC-induced phosphorylation of CD3epsilon and for recruitment of protein kinase Ctheta to the immune synapse in differentiated CD8+ T lymphocytes. However, whereas these two events are dispensable for functional T cell responsiveness to high-avidity ligands, they are required for responsiveness to low-avidity ones. Thus, in at least certain T cell clonotypes, the CD3epsilon PRS amplifies weak TCR signals by promoting synapse formation and CD3epsilon phosphorylation.

In vivo imaging of a diabetogenic CD8+ T cell response during type 1 diabetes progression

Type 1 diabetes is preceded by a long, protracted period of pancreatic islet inflammation by autoreactive lymphocytes. Noninvasive imaging of islet inflammation prior to the onset of hyperglycemia might have diagnostic and therapeutic implications, but this is not currently possible. Here, MRI is used to track, noninvasively, the accumulation diabetogenic CD8+ T-cells during type 1 diabetes progression in nonobese diabetic (NOD) mice. The contrast agent is an MRI probe (MN-NRP-V7) that specifically labels CD8+ T-cells recognizing residues 206-214 of islet-specific glucose-6-phosphatase catalytic subunit related protein (IGRP(206-214)) in the context of the major histocompatibility complex (MHC) class I molecule H-2K(d). This probe consists of superparamagnetic iron oxide nanoparticles (MN) coated with K(d) molecules presenting NRP-V7, a high-avidity mimotope of IGRP(206-214). NOD mice of different ages (5, 8, 15, and 24 weeks) were imaged by MRI before and after a single intravenous injection of MN-NRP-V7 or unmodified MN nanoparticles. MN-NRP-V7 accumulation, as determined by semiquantitative MRI analysis of pancreas-associated T(2) relaxation time, was antigen-specific, age-dependent, and well correlated with the numbers of MN-NRP-V7-labeled CD8+ T-cells recovered from the pancreata of the treated mice. Antigen/MHC-coupled nanoparticles represent a promising new avenue for noninvasive imaging of lymphocyte inflammation in organ-specific autoimmunity and transplantation.

Rotavirus infection accelerates type 1 diabetes in mice with established insulitis

Infection modulates type 1 diabetes, a common autoimmune disease characterized by the destruction of insulin-producing islet beta cells in the pancreas. Childhood rotavirus infections have been associated with exacerbations in islet autoimmunity. Nonobese diabetic (NOD) mice develop lymphocytic islet infiltration (insulitis) and then clinical diabetes, whereas NOD8.3 TCR mice, transgenic for a T-cell receptor (TCR) specific for an important islet autoantigen, show more rapid diabetes onset. Oral infection of infant NOD mice with the monkey rotavirus strain RRV delays diabetes development. Here, the effect of RRV infection on diabetes development once insulitis is established was determined. NOD and NOD8.3 TCR mice were inoculated with RRV aged > or = 12 and 5 weeks, respectively. Diabetes onset was significantly accelerated in both models (P < 0.024), although RRV infection was asymptomatic and confined to the intestine. The degree of diabetes acceleration was related to the serum antibody titer to RRV. RRV-infected NOD mice showed a possible trend toward increased insulitis development. Infected males showed increased CD8(+) T-cell proportions in islets. Levels of beta-cell major histocompatibility complex class I expression and islet tumor necrosis factor alpha mRNA were elevated in at least one model. NOD mouse exposure to mouse rotavirus in a natural experiment also accelerated diabetes. Thus, rotavirus infection after beta-cell autoimmunity is established affects insulitis and exacerbates diabetes. A possible mechanism involves increased exposure of beta cells to immune recognition and activation of autoreactive T cells by proinflammatory cytokines. The timing of infection relative to mouse age and degree of insulitis determines whether diabetes onset is delayed, unaltered, or accelerated.

Rapid identification of MHC class I-restricted antigens relevant to autoimmune diabetes using retrogenic T cells

The method described herein provides a novel strategy for the rapid identification of CD8(+) T cell epitopes relevant to type 1 diabetes in the context of the nonobese diabetic (NOD) mouse model of disease. Obtaining the large number of antigen-sensitive monospecific T cells required for conventional antigen discovery methods has historically been problematic due to (1) difficulties in culturing autoreactive CD8(+) T cells from NOD mice and (2) the large time and resource investments required for the generation of transgenic NOD mice. We circumvented these problems by exploiting the rapid generation time of retrogenic (Rg) mice, relative to transgenic mice, as a novel source of sensitive monospecific CD8(+) T cells, using the diabetogenic AI4 T cell receptor on NOD.SCID and NOD.Rag1(-/-) backgrounds as a model. Rg AI4 T cells are diabetogenic in vivo, demonstrating for the first time that Rg mice are a means for assessing the pathogenic potential of CD8(+) T cell receptor specificities. In order to obtain a sufficient number of Rg CD8(+) T cells for antigen screens, we optimized a method for their in vitro culture that resulted in a approximately 500 fold expansion. We demonstrate the high sensitivity and specificity of expanded Rg AI4 T cells in the contexts of (1) specific peptide challenge, (2) islet cytotoxicity, and (3) their ability to resolve previously defined mimotope candidates from a positional scanning peptide library. Our method is the first to combine the speed of Rg technology with an optimized in vitro Rg T cell expansion protocol to enable the rapid discovery of T cell antigens.

Identification of novel IGRP epitopes targeted in type 1 diabetes patients

CD8(+) T cells play an important role in the development of type 1 diabetes (T1D) in NOD mice and humans. IGRP (islet-specific glucose-6-phosphatase catalytic subunit-related protein) has emerged in recent years as a major antigen in NOD mice. Therefore, we aimed to determine if IGRP is an antigen in T1D patients and to identify the HLA-A2-restricted IGRP epitopes targeted. Using IFN-gamma ELISPOT assay, we tested PBMC from recent-onset pediatric T1D patients and healthy controls for reactivity to four IGRP peptides directly ex vivo. Importantly, 65% of patients and 0% of controls were positive for at least one IGRP peptide. Two of these have not been reported previously. These data provide evidence that IGRP is a CD8(+) T cell antigen in humans, contributing to the understanding of the underlying disease process as well as to future directions for diagnosis and monitoring disease progression in T1D patients.

Exendin-4 improves reversal of diabetes in NOD mice treated with anti-CD3 monoclonal antibody by enhancing recovery of beta-cells

Immune modulators can arrest loss of insulin secretion in type 1 diabetes mellitus (T1DM), but they have not caused permanent disease remission or restored normal insulin secretion. We tested whether exendin-4, a glucagon-like peptide-1 receptor agonist, would enhance remission of T1DM in NOD mice treated with anti-CD3 monoclonal antibody (mAb) and studied the effects of exendin-4 treatment on cellular and metabolic responses of beta-cells. Diabetic NOD mice treated with anti-CD3 mAb and exendin-4 had a higher rate of remission (44%) than mice treated with anti-CD3 mAb alone (37%) or exendin-4 (0%) or insulin or IgG alone (0%) (P < 0.01). The effect of exendin-4 on reversal of diabetes after anti-CD3 mAb was greatest in mice with a glucose level of less than 350 mg/dl at diagnosis (63 vs. 39%, P < 0.05). Exendin-4 did not affect beta-cell area, replication, or apoptosis or reduce the frequency of diabetogenic or regulatory T cells or modulate the antigenicity of islet cells. Reversal of T1DM with anti-CD3 mAb was associated with recovery of insulin in glucose transporter-2(+)/insulin(-) islet cells that were identified at diagnosis. Glucose tolerance and insulin responses improved in mice treated with combination therapy, and exendin-4 increased insulin content and insulin release from beta-cells. We conclude that treatment with glucagon-like peptide-1 receptor agonist enhances remission of T1DM in NOD mice treated with anti-CD3 mAb by enhancing the recovery of the residual islets. This combinatorial approach may be useful in treatment of patients with new-onset T1DM.

Adenosine deamination sustains dendritic cell activation in inflammation

Adenosine is a suppressive agent that protects the host from excessive tissue injury associated with strong inflammation. In tissue stress, higher levels of adenosine signal through adenosine receptors to exert strong anti-inflammatory effects, and thus protect host cells. Existing evidence also suggests that elevated adenosine potently down-regulates the activation of lymphocytes during inflammation. This notion, however, is in contrast with another basic observation that the immune system is highly activated precisely under the same circumstances against pathogens. In this study, we show that inflammatory responses of dendritic cells (DCs) are highly sensitive to adenosine suppression. However, they intrinsically carry high adenosine deaminase activity, which in turn degrades and removes adenosine from the surroundings, cutting off DCs from the suppression. This regulatory mechanism is important in DC responses to pathogen-associated molecular patterns and their activation of T cells. Our findings suggest a mechanism that DCs maintain their hyperreactive state in inflammation despite the general state of suppression, and reveal a regulatory role of adenosine deaminase in DC innate immune responses.

Use of baculovirus MHC/peptide display libraries to characterize T-cell receptor ligands

Peptide/protein display libraries are powerful tools for identifying and manipulating receptor/ligand pairs. While the large size of bacterial phage display libraries has made them the platform of choice in many applications, often considerable engineering has been required to achieve display of properly folded and active eukaryotic proteins, such as antibodies. This problem has been partially solved in several eukaryotic display systems, e.g. using yeast or retroviruses, but these systems have their own limitations. Recently, baculovirus has been developed as a display system using the virus itself or infected insect cells as the display platform. Here, we review the development and use of baculovirus-infected cells as a platform for display libraries of peptides bound to major histocompatibility complex (MHC) class I (MHCI) or class II (MHCII). We have used fluorescent multimeric soluble T-cell receptors (TCRs) to screen these libraries and to identify peptide antigen mimotopes. We also present some improvements to this system that allow very large libraries to be constructed and screened. We have used these libraries to examine the role of MHCII-bound peptides in the presentation of the staphylococcal enterotoxin A (SEA) and to manipulate an MHCI tumor-associated antigen.

Transient upregulation of indoleamine 2,3-dioxygenase in dendritic cells by human chorionic gonadotropin downregulates autoimmune diabetes

OBJECTIVE

Pregnancy induces a state of immunological tolerance that aims at suppressing immune responses against the fetus and has been linked to temporal remission of preexisting autoimmune disorders. To understand the mechanisms of this reversible immune regulation, we investigated the role of a key pregnancy hormone, human chorionic gonadotropin (hCG), in immune tolerance against autoimmune type 1 diabetes in nonobese diabetic (NOD) mice.

RESEARCH DESIGN AND METHODS

We injected hCG into cytokine gene-deficient NOD mice and evaluated the effects of hCG administration on T-cells and dendritic cells (DCs).

RESULTS

We show that administration of hCG to NOD mice inhibits both the activation of diabetogenic CD4(+) and CD8(+) T-cells, in vitro and in vivo, and the progression of type 1 diabetes by upregulating the expression of indoleamine 2,3-dioxygenase (IDO) in DCs. IDO upregulation is transient and declined shortly after hCG withdrawal. DC depletion restores the diabetetogenic activity of splenic T-cells from hCG-treated mice, and inhibition of IDO activity by 1-methyl-tryptophan abrogates the hCG-induced T-cell suppression and resistance to type 1 diabetes.

CONCLUSIONS

We propose that hCG-induced upregulation of IDO in DCs plays a major role in pregnancy-associated resistance to autoimmunity.

Efficient activation of Valpha14 invariant NKT cells by foreign lipid antigen is associated with concurrent dendritic cell-specific self recognition

A burst release of cytokines by Valpha14 invariant NKT (iNKT) cells upon their TCR engagement critically regulates innate and adaptive immune responses. However, it remains unclear in vivo why iNKT cells respond efficiently to microbial or intracellular lipid Ags that are at low levels or that possess suboptimal antigenicity. We found that dendritic cells (DCs) potentiated iNKT cells to respond to a minimal amount of ligand alpha-galactosylceramide (alphaGalCer) through CD1d-dependent autoreactive responses that require endosomal processing and CD1d trafficking. The ability of potentiation of NKT cells was DC specific and did not depend on costimulatory signals and IL-12 production by DCs. However, DCs that failed to synthesize a major endogenous lipid Ag isoglobotrihexosylceramide were unable to potentiate NKT cells for efficient activation. Further analysis showed that differences in the level and pattern of endogenous lipid Ag presentation differentiate DCs and B cells for effective potentiation and subsequent activation of iNKT cells in the presence of an exogenous Ag. Thus, CD1d-dependent potentiation by DCs may be crucial for iNKT cell-mediated immunity against infectious agents.

Identical beta cell-specific CD8(+) T cell clonotypes typically reside in both peripheral blood lymphocyte and pancreatic islets

A major issue regarding T cell responses in autoimmunity is how the repertoire compares between the periphery and target organ. In type 1 diabetes, the status of at-risk or diabetic individuals can be monitored by measuring beta cell-specific T cells isolated from PBL, but whether these T cells accurately reflect the repertoire residing in the pancreatic islets is unclear. The TCR repertoire of disease-relevant, tetramer-sorted CD8(+) T cells was examined at the single-cell level in PBL, pancreatic lymph nodes (PLN), and the islets of individual NOD mice. CDR3alpha and CDR3beta sequences demonstrated that the same repertoire of T cells in PBL was detected in the islets and PLN, although the frequency of specific clonotypes varied. Albeit infrequent, clonotypes that were prevalent in the islets but not found in PBL were also detected. beta cell Ag immunization expanded immunodominant PBL clonotypes present in the islets and PLN. These results show that insight into repertoire profiles of islet-infiltrating T cells can be obtained from PBL.

Interleukin-2 gene variation impairs regulatory T cell function and causes autoimmunity

Autoimmune diseases are thought to result from imbalances in normal immune physiology and regulation. Here, we show that autoimmune disease susceptibility and resistance alleles on mouse chromosome 3 (Idd3) correlate with differential expression of the key immunoregulatory cytokine interleukin-2 (IL-2). In order to test directly that an approximately twofold reduction in IL-2 underpins the Idd3-linked destabilization of immune homeostasis, we show that engineered haplodeficiency of Il2 gene expression not only reduces T cell IL-2 production by twofold but also mimics the autoimmune dysregulatory effects of the naturally occurring susceptibility alleles of Il2. Reduced IL-2 production achieved by either genetic mechanism correlates with reduced function of CD4(+) CD25(+) regulatory T cells, which are critical for maintaining immune homeostasis.

TRPV1+ sensory neurons control beta cell stress and islet inflammation in autoimmune diabetes

In type 1 diabetes, T cell-mediated death of pancreatic beta cells produces insulin deficiency. However, what attracts or restricts broadly autoreactive lymphocyte pools to the pancreas remains unclear. We report that TRPV1(+) pancreatic sensory neurons control islet inflammation and insulin resistance. Eliminating these neurons in diabetes-prone NOD mice prevents insulitis and diabetes, despite systemic persistence of pathogenic T cell pools. Insulin resistance and beta cell stress of prediabetic NOD mice are prevented when TRPV1(+) neurons are eliminated. TRPV1(NOD), localized to the Idd4.1 diabetes-risk locus, is a hypofunctional mutant, mediating depressed neurogenic inflammation. Delivering the neuropeptide substance P by intra-arterial injection into the NOD pancreas reverses abnormal insulin resistance, insulitis, and diabetes for weeks. Concordantly, insulin sensitivity is enhanced in trpv1(-/-) mice, whereas insulitis/diabetes-resistant NODxB6Idd4-congenic mice, carrying wild-type TRPV1, show restored TRPV1 function and insulin sensitivity. Our data uncover a fundamental role for insulin-responsive TRPV1(+) sensory neurons in beta cell function and diabetes pathoetiology.

Cytotoxic T-cells from T-cell receptor transgenic NOD8.3 mice destroy beta-cells via the perforin and Fas pathways

Cytotoxic T-cells are the major mediators of beta-cell destruction in type 1 diabetes, but the molecular mechanisms are not definitively established. We have examined the contribution of perforin and Fas ligand to beta-cell destruction using islet-specific CD8(+) T-cells from T-cell receptor transgenic NOD8.3 mice. NOD8.3 T-cells killed Fas-deficient islets in vitro and in vivo. Perforin-deficient NOD8.3 T-cells were able to destroy wild-type but not Fas-deficient islets in vitro. These results imply that NOD8.3 T-cells use both pathways and that Fas is required for beta-cell killing only when perforin is missing. Consistent with this theory, transgenic NOD8.3 mice with beta-cells that do not respond to Fas ligation were not protected from diabetes. We next investigated the mechanism of protection provided by overexpression of suppressor of cytokine signaling-1 (SOCS-1) in beta-cells of NOD8.3 mice. SOCS-1 islets remained intact when grafted into NOD8.3 mice and were less efficiently killed in vitro. However, addition of exogenous peptide rendered SOCS-1 islets susceptible to 8.3 T-cell-mediated lysis. Therefore, NOD8.3 T-cells use both perforin and Fas pathways to kill beta-cells and the surprising blockade of NOD8.3 T-cell-mediated beta-cell death by SOCS-1 overexpression may be due in part to reduced target cell recognition.

Lessons on autoimmune diabetes from animal models

T1DM (Type I diabetes mellitus) results from selective destruction of the insulin-producing beta-cells of the pancreas by the immune system, and is characterized by hyperglycaemia and vascular complications arising from suboptimal control of blood glucose levels. The discovery of animal models of T1DM in the late 1970s and early 1980s, particularly the NOD (non-obese diabetic) mouse and the BB (BioBreeding) diabetes-prone rat, had a fundamental impact on our ability to understand the genetics, aetiology and pathogenesis of this disease. NOD and BB diabetes-prone rats spontaneously develop a form of diabetes that closely resembles the human counterpart. Early studies of these animals quickly led to the realization that T1DM is caused by autoreactive T-lymphocytes and revealed that the development of T1DM is controlled by numerous polymorphic genetic elements that are scattered throughout the genome. The development of transgenic and gene-targeting technologies during the 1980s allowed the generation of models of T1DM of reduced genetic and pathogenic complexity, and a more detailed understanding of the immunogenetics of T1DM. In this review, we summarize the contribution of studies in animal models of T1DM to our current understanding of four fundamental aspects of T1DM: (i) the nature of genetic elements affording T1DM susceptibility or resistance; (ii) the mechanisms underlying the development and recruitment of pathogenic autoreactive T-cells; (iii) the identity of islet antigens that contribute to the initiation and/or progression of islet inflammation and beta-cell destruction; and (iv) the design of avenues for therapeutic intervention that are rooted in the knowledge gained from studies of animal models. Development of new animal models will ensure continued progress in these four areas.

The combined effects of tryptophan starvation and tryptophan catabolites down-regulate T cell receptor zeta-chain and induce a regulatory phenotype in naive T cells

Tryptophan catabolism is a tolerogenic effector system in regulatory T cell function, yet the general mechanisms whereby tryptophan catabolism affects T cell responses remain unclear. We provide evidence that the short-term, combined effects of tryptophan deprivation and tryptophan catabolites result in GCN2 kinase-dependent down-regulation of the TCR zeta-chain in murine CD8+ T cells. TCR zeta down-regulation can be demonstrated in vivo and is associated with an impaired cytotoxic effector function in vitro. The longer-term effects of tryptophan catabolism include the emergence of a regulatory phenotype in naive CD4+CD25- T cells via TGF-beta induction of the forkhead transcription factor Foxp3. Such converted cells appear to be CD25+, CD69-, CD45RBlow, CD62L+, CTLA-4+, BTLAlow and GITR+, and are capable of effective control of diabetogenic T cells when transferred in vivo. Thus, both tryptophan starvation and tryptophan catabolites contribute to establishing a regulatory environment affecting CD8+ as well as CD4+ T cell function, and not only is tryptophan catabolism an effector mechanism of tolerance, but it also results in GCN2-dependent generation of autoimmune-preventive regulatory T cells.

Islet-specific glucose-6-phosphatase catalytic subunit-related protein-reactive CD4+ T cells in human subjects

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is recognized as a major autoantigen for autoimmune type 1 diabetes (T1D) in the NOD mouse model. This study was undertaken to examine CD4+ T cell responses toward IGRP in human subjects. The tetramer-guided epitope mapping approach was used to identify IGRP-specific CD4+ T cell epitopes. IGRP(23-35) and IGRP(247-259) were identified as DRA1*0101/DRB1*0401-restricted epitopes. IGRP(13-25) and IGRP(226-238) were identified as DRA1*0101/DRB1*0301-restricted epitopes. IGRP-specific tetramers were used to evaluate the prevalence of IGRP-reactive T cells in healthy and T1D subjects. More than 80% of subjects with either DRB1*0401 or DRB1*0301 haplotype have IGRP-specific CD4+ T cell responses for at least one IGRP epitope. IGRP-specific T cells from both healthy and T1D groups produce both gamma-IFN and IL-10. DRA1*0101/DRB1*0401 IGRP(247-259)-restricted T cells also show cross-reactivity to an epitope derived from liver/kidney glucose-6-phosphatase. The detection of IGRP-reactive T cells in both type 1 diabetic subjects and healthy subjects and recent reports of other autoreactive T cells detected in healthy subjects underscore the prevalence of potentially autoreactive T cells in the peripheral immune system of the general population.

Early autoimmune destruction of islet grafts is associated with a restricted repertoire of IGRP-specific CD8+ T cells in diabetic nonobese diabetic mice

beta cell replacement via islet or pancreas transplantation is currently the only approach to cure type 1 diabetic patients. Recurrent beta cell autoimmunity is a critical factor contributing to graft rejection along with alloreactivity. However, the specificity and dynamics of recurrent beta cell autoimmunity remain largely undefined. Accordingly, we compared the repertoire of CD8+ T cells infiltrating grafted and endogenous islets in diabetic nonobese diabetic mice. In endogenous islets, CD8+ T cells specific for an islet-specific glucose-6-phosphatase catalytic subunit-related protein derived peptide (IGRP206-214) were the most prevalent T cells. Similar CD8+ T cells dominated the early graft infiltrate but were expanded 6-fold relative to endogenous islets. Single-cell analysis of the TCR alpha and beta chains showed restricted variable gene usage by IGRP206-214-specific CD8+ T cells that was shared between the graft and endogenous islets of individual mice. However, as islet graft infiltration progressed, the number of IGRP206-214-specific CD8+ T cells decreased despite stable numbers of CD8+ T cells. These results demonstrate that recurrent beta cell autoimmunity is characterized by recruitment to the grafts and expansion of already prevalent autoimmune T cell clonotypes residing in the endogenous islets. Furthermore, depletion of IGRP206-214-specific CD8+ T cells by peptide administration delayed islet graft survival, suggesting IGRP206-214-specific CD8+ T cells play a role early in islet graft rejection but are displaced with time by other specificities, perhaps by epitope spread.

The NOD mouse: a model of immune dysregulation

Autoimmunity is a complex process that likely results from the summation of multiple defective tolerance mechanisms. The NOD mouse strain is an excellent model of autoimmune disease and an important tool for dissecting tolerance mechanisms. The strength of this mouse strain is that it develops spontaneous autoimmune diabetes, which shares many similarities to autoimmune or type 1a diabetes (T1D) in human subjects, including the presence of pancreas-specific autoantibodies, autoreactive CD4+ and CD8+ T cells, and genetic linkage to disease syntenic to that found in humans. During the past ten years, investigators have used a wide variety of tools to study these mice, including immunological reagents and transgenic and knockout strains; these tools have tremendously enhanced the study of the fundamental disease mechanisms. In addition, investigators have recently developed a number of therapeutic interventions in this animal model that have now been translated into human therapies. In this review, we summarize many of the important features of disease development and progression in the NOD strain, emphasizing the role of central and peripheral tolerance mechanisms that affect diabetes in these mice. The information gained from this highly relevant model of human disease will lead to potential therapies that may alter the development of the disease and its progression in patients with T1D.

Characterization of the anti-tissue transglutaminase antibody response in nonobese diabetic mice

Type 1 diabetes mellitus is an autoimmune disorder characterized by destruction of insulin-producing pancreatic beta cells by T lymphocytes. In nonobese diabetic (NOD) mice, a role has been hypothesized for dietary gluten proteins in the onset of diabetes, and because gluten dependence is the major feature of celiac disease, together with production of Abs to the autoantigen tissue transglutaminase (tTG), we looked for the presence of anti-tTG Abs in the serum of NOD mice and, to establish their origin, analyzed the Ab repertoire of NOD mice using phage display Ab libraries. We found significant levels of serum anti-tTG Abs and were able to isolate single-chain Ab fragments to mouse tTG mainly from the Ab libraries made from intestinal lymphocytes and to a lesser extent from splenocytes. Data from NOD mice on a gluten-free diet suggest that the anti-tTG response is not gluten-dependent. The intestinal Ab response to tTG is a feature of NOD mice, but the underlying mechanisms remain obscure.

Developmental control of CD8 T cell-avidity maturation in autoimmune diabetes

The progression of immune responses is generally associated with an increase in the overall avidity of antigen-specific T cell populations for peptide-MHC. This is thought to result from preferential expansion of high-avidity clonotypes at the expense of their low-avidity counterparts. Since T cell antigen-receptor genes do not mutate, it is puzzling that high-avidity clonotypes do not predominate from the outset. Here we provide a developmental basis for this phenomenon in the context of autoimmunity. We have carried out comprehensive studies of the diabetogenic CD8 T cell population that targets residues 206-214 of the beta cell antigen islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP(206-214)) and undergoes avidity maturation as disease progresses. We find that the succession of IGRP(206-214)-specific clonotypes with increasing avidities during the progression of islet inflammation to overt diabetes in nonobese diabetic mice is fueled by autoimmune inflammation but opposed by systemic tolerance. As expected, naive high-avidity IGRP(206-214)-specific T cells respond more efficiently to antigen and are significantly more diabetogenic than their intermediate- or low-avidity counterparts. However, central and peripheral tolerance selectively limit the contribution of these high-avidity T cells to the earliest stages of disease without abrogating their ability to progressively accumulate in inflamed islets and kill beta cells. These results illustrate the way in which incomplete deletion of autoreactive T cell populations of relatively high avidity can contribute to the development of pathogenic autoimmunity in the periphery.

Prevention of diabetes by manipulation of anti-IGRP autoimmunity: high efficiency of a low-affinity peptide

Antigen therapy may hold great promise for the prevention of autoimmunity; however, most clinical trials have failed, suggesting that the principles guiding the choice of treatment remain ill defined. Here, we examine the antidiabetogenic properties of altered peptide ligands of CD8+ T cells recognizing an epitope of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP206-214), a prevalent population of autoreactive T cells in autoimmune diabetes. We show that islet-associated CD8+ T cells in nonobese diabetic mice recognize numerous IGRP epitopes, and that these cells have a role in the outcome of protocols designed to induce IGRP206-214-specific tolerance. Ligands targeting IGRP206-214-reactive T cells prevented disease, but only at doses that spared low-avidity clonotypes. Notably, near complete depletion of the IGRP206-214-reactive T-cell pool enhanced the recruitment of subdominant specificities and did not blunt diabetogenesis. Thus, peptide therapy in autoimmunity is most effective under conditions that foster occupation of the target organ lymphocyte niche by nonpathogenic, low-avidity clonotypes.

Identification of CD4+ T Cell-Specific Epitopes of Islet-Specific Glucose-6-Phosphatase Catalytic Subunit-Related Protein: A Novel β Cell Autoantigen in Type 1 Diabetes

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) has been identified as a novel CD8(+) T cell-specific autoantigen in NOD mice. This study was undertaken to identify MHC class II-specific CD4(+) T cell epitopes of IGRP. Peptides named P1, P2, P3, P4, P5, P6, and P7 were synthesized by aligning the IGRP protein amino acid sequence with peptide-binding motifs of the NOD MHC class II (I-A(g7)) molecule. Peptides P1, P2, P3, and P7 were immunogenic and induced both spontaneous and primed responses. IGRP peptides P1-, P2-, P3-, and P7-induced responses were inhibited by the addition of anti-MHC class II (I-A(g7)) Ab, confirming that the response is indeed I-A(g7) restricted. Experiments using purified CD4(+) and CD8(+) T cells from IGRP peptide-primed mice also showed a predominant CD4(+) T cell response with no significant activation of CD8(+) T cells. T cells from P1-, P3-, and P7-primed mice secreted both IFN-gamma and IL-10 cytokines, whereas P2-primed cells secreted only IFN-gamma. Peptides P3 and P7 prevented the development of spontaneous diabetes and delayed adoptive transfer of diabetes. Peptides P1 and P2 delayed the onset of diabetes in both these models. In summary, we have identified two I-A(g7)-restricted CD4(+) T cell epitopes of IGRP that can modulate and prevent the development of diabetes in NOD mice. These results provide the first evidence on the role of IGRP-specific, MHC class II-restricted CD4(+) T cells in disease protection and may help in the development of novel therapies for type 1 diabetes.

Crystallization and preliminary X-ray structural studies of a high-affinity CD8alphaalpha co-receptor to pMHC

The class I CD8 positive T-cell response is involved in a number of conditions in which artificial down-regulation and control would be therapeutically beneficial. Such conditions include a number of autoimmune diseases and graft rejection in transplant patients. Although the CD8 T-cell response is dominated by the TCR-pMHC interaction, activation of T cells is in most cases also dependent on a number of associated signalling molecules. Previous work has demonstrated the ability of one such molecule (CD8) to act as an antagonist to T-cell activation if added in soluble form. Therefore, a high-affinity mutant CD8 (haCD8) has been developed with the aim of developing a therapeutic immunosuppressor. In order to fully understand the nature of the haCD8 interaction, this protein was crystallized using the sitting-drop vapour-diffusion method. Single haCD8 crystals were cryocooled and used for data collection. These crystals belonged to space group P6(4)22 (assumed by similarity to the wild type), with unit-cell parameters a = 101.08, c = 56.54 A. VM calculations indicated one molecule per asymmetric unit. A 2 A data set was collected and the structure is currently being determined using molecular replacement.

Using a baculovirus display library to identify MHC class I mimotopes

We have developed a baculovirus-based display system for identifying antigen mimotopes for MHC class I-specific T cells. The mouse MHC class I molecule, Dd, was displayed on baculovirus-infected insect cells with a library of 9- and 10-mer peptides tethered via a flexible linker to the N terminus of beta2 microglobulin. As a test case, the library was screened by flow cytometry by using a multimeric fluorescent alphabetaTCR from a mouse T cell specific for Dd plus an unknown self peptide. A mimotope was identified that, when bound to Dd, stimulated the T cell to secret IL-2. The sequence of the mimotope was used to identify a self peptide present in a mouse protein, Spin. The Spin peptide, when complexed with Dd, also activated the T cell. This technique should be generally useful in identifying and manipulating MHC class I peptide mimotopes and epitopes.

Satisfaction (not) guaranteed: re-evaluating the use of animal models of type 1 diabetes

Without a doubt, rodent models have been instrumental in describing pathways that lead to pancreatic beta-cell destruction, evaluating potential causes of type 1 diabetes and providing proof-of-principle for the potential of immune-based interventions. However, despite more than two decades of productive research, we are still yet to define an initiating autoantigen for the human disease, to determine the precise mechanisms of beta-cell destruction in humans and to design interventions that prevent or cure type 1 diabetes. In this Perspective article, we propose that a major philosophical change would benefit this field, a proposition that is based on evaluation of situations in which rodent models have provided useful guidance and in which they have led to disappointments.

IL-10 Diminishes CTLA-4 Expression on Islet-Resident T Cells and Sustains Their Activation Rather Than Tolerance

IL-10, a powerful anti-Th1 cytokine, has shown paradoxical effects against diabetes. The mechanism underlying such variable function remains largely undefined. An approach for controlled mobilization of endogenous IL-10 was applied to the NOD mouse and indicated that IL-10 encounter with diabetogenic T cells within the islets sustains activation, while encounter occurring peripheral to the islets induces tolerance. Insulin beta-chain (INSbeta) 9-23 peptide was expressed on an Ig, and the aggregated (agg) form of the resulting Ig-INSbeta triggered IL-10 production by APCs, and expanded IL-10-producing T regulatory cells. Consequently, agg Ig-INSbeta delayed diabetes effectively in young NOD mice whose pathogenic T cells remain peripheral to the islets. However, agg Ig-INSbeta was unable to suppress the disease in 10-wk-old insulitis-positive animals whose diabetogenic T cells have populated the islets. This is not due to irreversibility of the disease because soluble Ig-INSbeta did delay diabetes in these older mice. Evidence is provided indicating that upon migration to the islet, T cells were activated and up-regulated CTLA-4 expression. IL-10, however, reverses such up-regulation, abolishing CTLA-4-inhibitory functions and sustaining activation of the islet T lymphocytes. Therefore, IL-10 supports T cell tolerance in the periphery, but its interplay with CTLA-4 sustains activation within the islets. As a result, IL-10 displays opposite functions against diabetes in young vs older insulitis-positive mice.

Pathogenic T-cell clones in autoimmune diabetes: more lessons from the NOD mouse

T-cell clones that can efficiently transfer diabetes to prediabetic nonobese diabetic (NOD) mice provide a powerful approach to dissecting the autoimmune disease process and for investigating immunoregulation. Diabetogenic T-cell clones carried in culture allow for detailed analysis of T-cell effector function and in vivo activity, and thus the contribution of a single clonotype to pathogenesis can be studied. As T cells comprising most or all of the repertoire in T-cell receptor transgenic (TCR-Tg) mice, diabetogenic T-cell clones have led to new variations on the NOD mouse model of autoimmune disease. T-cell clones are being used to screen peptide libraries and proteomic arrays to identify the autoantigens that drive these clones in vivo and to extend our knowledge of the processes that give rise to these antigens. With the identification of peptide agonists and natural ligands, the development of MHC-peptide multimers has been possible. These reagents can track T cells in vivo and thus provide new approaches for disease diagnosis and therapy as well as a versatile set of tools for basic research on how T cells contribute to autoimmune disease.

CTLA-4-Ig activates forkhead transcription factors and protects dendritic cells from oxidative stress in nonobese diabetic mice

Prediabetes and diabetes in nonobese diabetic (NOD) mice have been targeted by a variety of immunotherapies, including the use of a soluble form of cytotoxic T lymphocyte antigen 4 (CTLA-4) and interferon (IFN)-gamma. The cytokine, however, fails to activate tolerogenic properties in dendritic cells (DCs) from highly susceptible female mice early in prediabetes. The defect is characterized by impaired induction of immunosuppressive tryptophan catabolism, is related to transient blockade of the signal transducer and activator of transcription (STAT)1 pathway of intracellular signaling by IFN-gamma, and is caused by peroxynitrite production. Here, we show that soluble CTLA-4 imparts suppressive properties to DCs from early prediabetic NOD female mice through mechanisms that rely on autocrine signaling by IFN-gamma. Although phosphorylation of STAT1 in response to IFN-gamma is compromised in those mice, CTLA-4 obviates the defect. IFN-gamma-driven expression of tryptophan catabolism by CTLA-4-immunoglobulin is made possible through the concomitant activation of the Forkhead Box class O (FOXO) transcription factor FOXO3a, induction of the superoxide dismutase gene, and prevention of peroxynitrite formation.

Peptides from common viral and bacterial pathogens can efficiently activate diabetogenic T-cells

Cross-reactivity between an autoantigen and unknown microbial epitopes has been proposed as a molecular mechanism involved in the development of insulin-dependent diabetes (type 1 diabetes). Type 1 diabetes is an autoimmune disease that occurs in humans and the nonobese diabetic (NOD) mouse. BDC2.5 is an islet-specific CD4+ T-cell clone derived from the NOD mouse whose natural target antigen is unknown. A biometrical analysis of screening data from BDC2.5 T-cells and a positional scanning synthetic combinatorial library (PS-SCL) was used to analyze and rank all peptides in public viral and bacterial protein databases and identify potential molecular mimic sequences with predicted reactivity. Selected sequences were synthesized and tested for stimulatory activity with BDC2.5 T-cells. Active peptides were identified, and some of them were also able to stimulate spontaneously activated T-cells derived from young, pre-diabetic NOD mice, indicating that the reactivity of the BDC2.5 T-cell is directed at numerous mouse peptides. Our results provide evidence for their possible role as T-cell ligands involved in the activation of diabetogenic T-cells.

Suppressor of cytokine signaling-1 overexpression protects pancreatic beta cells from CD8+ T cell-mediated autoimmune destruction

In type 1 diabetes, cytokine action on beta cells potentially contributes to beta cell destruction by direct cytotoxicity, inducing Fas expression, and up-regulating class I MHC and chemokine expression to increase immune recognition. To simultaneously block beta cell responsiveness to multiple cytokines, we overexpressed suppressor of cytokine signaling-1 (SOCS-1). This completely prevented progression to diabetes in CD8(+) TCR transgenic nonobese diabetic (NOD) 8.3 mice without affecting pancreas infiltration and partially prevented diabetes in nontransgenic NOD mice. SOCS-1 appeared to protect at least in part by inhibiting TNF- and IFN-gamma-induced Fas expression on beta cells. Fas expression was up-regulated on beta cells in vivo in prediabetic NOD8.3 mice, and this was inhibited by SOCS-1. Additionally, IFN-gamma-induced class I MHC up-regulation and TNF- and IFN-gamma-induced IL-15 expression by beta cells were inhibited by SOCS-1, which correlated with suppressed 8.3 T cell proliferation in vitro. Despite this, 8.3 T cell priming in vivo appeared unaffected. Therefore, blocking beta cell responses to cytokines impairs recognition by CD8(+) T cells and blocks multiple mechanisms of beta cell destruction, but does not prevent T cell priming and recruitment to the islets. Our findings suggest that increasing SOCS-1 expression may be useful as a strategy to block CD8(+) T cell-mediated type 1 diabetes as well as to more generally prevent cytokine-dependent tissue destruction in inflammatory diseases.

Requirement for Both H-2Db and H-2Kd for the Induction of Diabetes by the Promiscuous CD8+ T Cell Clonotype AI4

The NOD mouse is a model for autoimmune type 1 diabetes in humans. CD8(+) T cells are essential for the destruction of the insulin-producing pancreatic beta cells characterizing this disease. AI4 is a pathogenic CD8(+) T cell clone, isolated from the islets of a 5-wk-old female NOD mouse, which is capable of mediating overt diabetes in the absence of CD4(+) T cell help. Recent studies using MHC-congenic NOD mice revealed marked promiscuity of the AI4 TCR, as the selection of this clonotype can be influenced by multiple MHC molecules, including some class II variants. The present work was designed, in part, to determine whether similar promiscuity also characterizes the effector function of mature AI4 CTL. Using splenocyte and bone marrow disease transfer models and in vitro islet-killing assays, we report that efficient recognition and destruction of beta cells by AI4 requires the beta cells to simultaneously express both H-2D(b) and H-2K(d) class I MHC molecules. The ability of the AI4 TCR to interact with both H-2D(b) and H-2K(d) was confirmed using recombinant peptide libraries. This approach also allowed us to define a mimotope peptide recognized by AI4 in an H-2D(b)-restricted manner. Using ELISPOT and mimotope/H-2D(b) tetramer analyses, we demonstrate for the first time that AI4 represents a readily detectable T cell population in the islet infiltrates of prediabetic NOD mice. Our identification of a ligand for AI4-like T cells will facilitate further characterization and manipulation of this pathogenic and promiscuous T cell population.

Tracking the recruitment of diabetogenic CD8+ T-cells to the pancreas in real time

Development of autoimmune diabetes in both humans and mice is preceded by a prolonged period of inflammation of pancreatic islets by autoreactive T-cells. Noninvasive imaging techniques, including positron-emission tomography and optical or magnetic resonance imaging, have been used to track the recruitment of lymphocytes to sites of inflammation. These techniques, however, rely on labeling strategies that are non-antigen specific and do not allow specific tracking of the recruitment of autoreactive lymphocytes. Here we describe an antigen-specific magnetic label to selectively target a prevalent population of diabetogenic CD8(+) T-cells that contribute to the progression of insulitis to overt diabetes in NOD mice. Superparamagnetic nanoparticles coated with multiple copies of a high-avidity peptide/major histocompatibility complex ligand of these T-cells (NRP-V7/K(d)) are endocytosed by CD8(+) T-cells in an antigen-specific manner. Using these T-cells as probes, we show that inflammation of pancreatic islets by autoreactive T-cells can be detected in real time by magnetic resonance imaging. This study demonstrates the feasibility of visualizing the presence of ongoing autoimmune responses noninvasively.

Regulation of autoimmune diabetes by complete Freund's adjuvant is mediated by NK cells

Autoimmune (type 1) diabetes results from a loss of beta cells that is mediated by self-reactive T cells. Previous studies have shown that a single injection of CFA prevents diabetes in nonobese diabetic (NOD) mice, but the mechanism(s) of protection remain unknown. We show here that NOD mice immunized with CFA have a markedly reduced incidence of diabetes and that this reduced incidence is associated with a decrease in the number of beta cell-specific, autoreactive CTL. In addition, the adoptive transfer of diabetes into syngeneic NOD/SCID recipients was prevented by CFA immunization, and the protective effects of CFA were lost when cells expressing the NK cell marker, asialo GM1, were removed from both donor cells and recipient mice. Returning a population of CD3-DX5+ cells to the adoptive transfer restored the protective effects of CFA. Therefore, NK cells mediate the protective effects of CFA possibly through the down-regulation of autoreactive CTL and stimulation of NK cells represents a novel approach to the prevention of autoimmune diabetes.

T-cell epitopes in type 1 diabetes

Type 1 diabetes (TID) results from T-cell-mediated destruction of pancreatic b cells in genetically predisposed individuals. Autoreactive CD4(+) T helper cells and CD8(+) cytotoxic T lymphocytes (CTLs) recognize b-cell-derived peptides in the context of major histocompatibility complex class II and I molecules, respectively, in a process that terminates in b-cell death. Many peptide epitopes derived from b-cell proteins have been described for both humans and the nonobese diabetic (NOD) mouse, but their relative importance in disease pathogenesis is unclear. The significance of identifying key b-cell epitopes is underscored by a study showing that in the NOD mouse monitoring of a single population of b-cell-specific CTLs in the peripheral blood using a high-avidity analogue of the endogenous peptide may be used to accurately predict diabetes occurrence. Future studies focused on the discovery of immunodominant b-cell epitopes and their high-avidity analogues should have considerable implications for prediction and immunotherapy of TID.

Allelic variation in class I K gene as candidate for a second component of MHC-linked susceptibility to type 1 diabetes in non-obese diabetic mice

AIMS/HYPOTHESIS

Recent studies have revealed that MHC-linked susceptibility to Type 1 diabetes is determined by multiple components. In the non-obese diabetic (NOD) mouse, a second component (Idd16) has been mapped to a region adjacent to, but distinct from Idd1 in the class II region. In this study, we investigated the class I K gene as a candidate gene for Idd16.

METHODS

We determined the genomic sequences of the class I K gene as well as the reactivity of K molecules with monoclonal antibodies in the NOD mouse, the Cataract Shionogi (CTS) mouse, and the NOD.CTS-H-2 congenic strain, which possesses a resistance allele to Type 1 diabetes at the Idd16 on the NOD genetic background genes.

RESULTS

While the K sequence of the NOD mouse was identical to that of Kd type, ten nucleotide substitutions were identified in the CTS mouse compared with the NOD mouse. Of these, three were in exon 4, giving two amino acid substitutions, which were identical to those seen in KK type. These characteristics were retained in the NOD.CTS-H-2 congenic strain, which had a lower incidence and delayed onset of Type 1 diabetes owing to a resistance allele at Idd16. Lymphocytes from NOD.CTS-H2 congenic mice reacted with anti-Kd and anti-Kk monoclonal antibodies, reflecting the unique sequence of the K gene. The nucleotide sequence of the K gene in the non-obese non-diabetic (NON) mouse was also unique, consisting of a combination of Kk- and Kb-like sequences.

CONCLUSIONS/INTERPRETATION

These data suggest that H2-K is unique in CTS and NON mice, and that allelic variation of the class I K gene may be responsible for Idd16.

Cross-priming of diabetogenic T cells dissociated from CTL-induced shedding of beta cell autoantigens

Cross-presentation of self Ags by APCs is key to the initiation of organ-specific autoimmunity. As MHC class I molecules are essential for the initiation of diabetes in nonobese diabetic (NOD) mice, we sought to determine whether the initial insult that allows cross-presentation of beta cell autoantigens in diabetes is caused by cognate interactions between naive CD8(+) T cells and beta cells. Naive splenic CD8(+) T cells from transgenic NOD mice expressing a diabetogenic TCR killed peptide-pulsed targets in the absence of APCs. To ascertain the role of CD8(+) T cell-induced beta cell lysis in the initiation of diabetes, we expressed a rat insulin promoter (RIP)-driven adenovirus E19 transgene in NOD mice. RIP-E19 expression inhibited MHC class I transport exclusively in beta cells and rendered these cells resistant to lysis by CD8(+) (but not CD4(+)) T cells, both in vitro and in vivo. Surprisingly, RIP-E19 expression impaired the accumulation of CD8(+) T cells in islets and delayed the onset of islet inflammation, without affecting the timing or magnitude of T cell cross-priming in the pancreatic lymph nodes, which is the earliest known event in diabetogenesis. These results suggest that access of beta cell autoantigens to the cross-presentation pathway in diabetes is T cell independent, and reveal a previously unrecognized function of MHC class I molecules on target cells in autoimmunity: local retention of disease-initiating clonotypes.

Kinetic evolution of a diabetogenic CD8+ T cell response

Nonobese diabetic (NOD) mice develop overt diabetes following prolonged periods of pancreatic islet inflammation involving both CD4+ and CD8+ T cells. The initiation and progression of autoimmune diabetes require the recruitment of beta cell-reactive CD8+ T cells to the pancreatic lymph nodes, their activation by antigen, and their subsequent migration into pancreatic islets. We and others have shown that a significant fraction of NOD islet-associated CD8+ T cells express highly homologous TCRalpha chains (Valpha17 and Jalpha42 joined by the same N-region sequence) and that they recognize the peptide NRP-A7 in the context of the MHC class I molecule H-2K(d). We have also shown that this T cell subpopulation undergoes a process of "avidity maturation" that is associated with progression of benign insulitis to overt diabetes. This paper will summarize our current understanding of the mechanisms that drive the recruitment and activation of this CD8+ T cell subpopulation.

Identification of a beta-cell-specific HLA class I restricted epitope in type 1 diabetes

Type 1 diabetes is an autoimmune disease in which pancreatic beta-cells are destroyed by cytotoxic T-cells that recognize peptide epitopes presented by HLA class I molecules. The identification of human beta-cell epitopes may significantly improve the prospects for immunodiagnosis and immunotherapy in type 1 diabetes. Using algorithms to predict nonameric beta-cell peptides that would bind to the common HLA allele, HLA-A*0201, we identified a potential epitope from the leader sequence of islet amyloid polypeptide (human islet amyloid polypeptide [IAPP] precursor protein [preproIAPP] 5-13: KLQVFLIVL). Peripheral blood mononuclear cells (PBMCs) were isolated from 18 HLA-A*0201 patients with type 1 diabetes (9 with recent-onset [<180 days; range, 1-120 days] and 9 with long-standing diabetes [>180 days; range, 183-3,273 days]) and 9 healthy, nondiabetic control subjects. PBMCs were screened for peptide recognition using interferon-gamma enzyme-linked immunospot (ELISpot) assays. Of the nine patients with recent-onset type 1 diabetes, six had ELISpot responses to preproIAPP 5-13 that were >3 SDs above the mean of the nondiabetic control subjects (P = 0.002). In contrast, no patients with type 1 diabetes for >180 days had a response above this threshold. In summary, preproIAPP 5-13 is a novel HLA class I epitope recognized by a significant proportion of cytotoxic T-cells from HLA-A*0201 patients with recent-onset type 1 diabetes and may prove to be a useful tool for the prediction and/or prevention of this disease.

Dissecting autoimmune diabetes through genetic manipulation of non-obese diabetic mice

Type 1 diabetes results from a genetically and immunologically complex autoimmune process that is specifically directed against the pancreatic beta cells. Non-obese diabetic mice spontaneously develop a form of autoimmune diabetes closely resembling the disease in humans. This happens because, like human diabetic patients, non-obese diabetic mice have an unfortunate combination of apparently normal alleles at numerous loci associated with Type 1 diabetes. In isolation, each of these allelic variants affords a small degree of susceptibility to diabetes. In combination, however, they set in motion a series of immunological events that lead to islet inflammation and overt diabetes. Type 1 diabetes is associated with defects in self-tolerance and immunoregulation. It involves presentation of beta cell antigens to autoreactive T lymphocytes by professional antigen-presenting cells, the recruitment of antigen-activated T cells into pancreatic islets, and the differentiation of these antigen-activated lymphocytes into beta cell killers. Understanding the precise sequence of events in the pathogenesis of Type 1 diabetes has been, and remains, a challenging task. Much of our understanding of the immunology of the disease stems from studies of genetically engineered, non-obese diabetic mice. These mice provide reductionist systems, with which the contribution of individual cellular elements, molecules or genes to the disease process can be dissected. This review focuses on the lessons that have been learned through studies of these mice.

Modulation of tryptophan catabolism by regulatory T cells

Regulatory T (T(R)) cells manifest constitutive expression of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), but the function of CTLA-4 in mediating the regulatory function of T(R) cells is unclear. We show here that mouse CD4+CD25+ cells, either resting or induced to overexpress CTLA-4 by treatment with antibody to CD3, initiated tryptophan catabolism in dendritic cells through a CTLA-4-dependent mechanism. This process required B7 expression and cytokine production by the dendritic cells. In contrast, T(R) cells cultured in the presence of bacterial lipopolysaccharide induced tryptophan catabolism by dendritic cells in a CTLA-4-independent but cytokine-dependent way. Thus, regulation of immunosuppressive tryptophan catabolism in dendritic cells might represent a major mechanism of action of T(R) cells.